1. Field of the Invention
The present invention relates to a media advancement mechanism of printers and more particularly to an advancement mechanism which provides a fine adjustment of the media in order to line up information on a preprinted form.
2. Description of the Prior Art
U.S. Pat. No. 3,986,594, entitled Serial Impact Calculator Printer, issued to Nicholas Kondur, Jr. on Oct. 19, 1976, teaches a serial impact printer of the type utilizing a dot matrix print head that is specifically adaptable for use as a calculator or adding machine and is characterized by utilizing a common drive source to advance the print head across the paper, advance the paper between printing operations, and selectively advance the inked ribbon between the ribbon supply spool and takeup spool. An improved paper-advancing apparatus has been devised which operates in close correlation with the print head drive member to provide a relatively high speed, simplified and inexpensive printer unit. The ribbon supply spools are so constructed and arranged as to be interchangeable and to permit direct drive through a spool-engaging member on the print head whereby to advance the inked ribbon in direct response to print head travel.
Paper-advancing rolls, including a platen and pressure roll are arranged in closely spaced, parallel relation to the cylindrical drive member for the print head, one of the rolls being incrementally driven by a drive pawl eccentrically mounted on the print head drive whereby to index the recording medium at the end of each printing cycle of the print head. The drive pawl selectively interengages with a ratchet on one of the paper-advancing rolls to overcome a detent which releasably engages one of the paper-advancing rolls to station the recording medium securely in position during the printing operation. In turn, the detent as well as the paper-advancing rolls are manually releasable to permit manual positioning or adjustment of the recording medium. The recording paper advances between the paperadvancing rolls along a resilient guide path which is so arranged as to accurately guide the paper between the rolls and to firmly support it in an upright position during the printing operation.
The above described apparatus for advancing the media in the printer is inadequate because the media can only be advanced in steps that correspond to each tooth of the ratchet wheel. Other than this one problem this apparatus is a good and inexpensive mechanism for advancing the media.